The broad objective of the proposed research is to determine the biological roles of Z-disk proteins, including alpha-actinin, and M-line proteins in straited muscle and in other biological movement systems. Z-disk proteins, such as alpha-actinin, may function 1) to anchor actin filaments to Z-disks or basal bodies in other movement systems and thereby provide a base from which actin filaments can produce movement; 2) to act together with M-line proteins in assembly of functional thick filaments and myofibrils or in controlling state of polymerization of actin in nonmuscle movement systems; or 3) to alter the functional role of actin filaments in movement. The specific objectives of this research are: 1) to specify the nature of the proteins constituting Z-disks and M-lines in striated muscle or their analogues in nonmuscle systems; these efforts will use selective extractions, biochemical characterization, and localization of antibody binding with light and electron microscopes; 2) to determine whether alpha-actinin and other Z-disk proteins can affect ability of actinin filaments to bind myosin and produce movement; these experiments will involve assays of the effects alpha-actinin on structure of actinin monomers while they are aggregated in filaments; 3) to ascertain the role of M-line and Z-disk proteins in assembly of myofibrils in differentiating myogenic cell cultures; this objective will involve determination of the temporal sequence of synthesis and assembly of different myofibrillar proteins by using rate of decrease of specific radioactivity in different proteins isolated from pulse-labeled myogenic cultures and by localizing binding of antibodies to M-line and Z-disk proteins at different stages of differentiation in myogenic cell cultures; and 4) to determine the role of Z-disk proteins in disassembly of myofibrils during metabolic turnover; this objective will involve studies of endogenous Ca 2 ion -activated protease that degrades Z-disks and characterization of this protease and other muscle proteases that may be involved in myofibrillar protein turnover.